Texas Instruments SN74LV138AD

Overview

SN74LV138AD from Texas Instruments is a 3-line to 8-line decoder/demultiplexer IC operating from 2 V to 5.5 V, featuring 9.5 ns maximum propagation delay at 5 V, active-low G0/G1 and active-high G2 enable inputs, and Ioff support for partial-power-down mode - used in memory decoding, LED matrix control, and 7-segment display addressing.

For engineers reviewing the SN74LV138AD datasheet, SN74LV138AD pinout, SN74LV138AD application, or SN74LV138AD equivalent, key selection criteria include VCC range compatibility (2–5.5 V), enable input logic polarity (G0/G1 low-active, G2 high-active), output drive capability (±12 mA at 5 V), thermal performance (RθJA = 73°C/W in SOIC-16), and Ioff-enabled system power sequencing.

Technical Context

The SN74LV138AD implements standard CMOS logic with balanced push-pull outputs and dedicated enable architecture: two active-low (G0, G1) and one active-high (G2) enables allow hierarchical expansion without external inverters. Its binary-select inputs (A0–A2) decode to eight active-low outputs (Y0–Y7), with all outputs disabled when any enable condition fails.

Designed for high-speed memory-decoding applications, it achieves sub-10 ns tpd at 5 V with 15 pF load and supports mixed-mode voltage operation across ports. The integrated Ioff circuitry ensures zero current backflow during partial power-down, meeting JESD17 latch-up >250 mA.

Key Specifications

Pinout & Package

SN74LV138AD is supplied in a 16-pin SOIC (D) package measuring 9.90 mm × 3.91 mm, with standard 1.27 mm pitch and gull-wing leads. Thermal resistance is 73°C/W (junction-to-ambient).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-to-8 decoder applications.

Compared with SN74LV138AD, the 74HC138DR lacks Ioff and has looser timing, limiting use in modern low-voltage or power-gated systems; the SN74LVC138APW offers identical functionality in a smaller, thermally superior TSSOP package but requires layout revision.

Availability

SN74LV138AD is available at Aetrix Electronics and suitable for memory address decoding, LED matrix control, 7-segment display multiplexing, and 8-bit data storage applications requiring stable component supply, long-term industrial lifecycle support, and consistent parametric performance.

Supply support for SN74LV138AD includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader delivering analog, embedded processing, and logic solutions with emphasis on reliability, scalability, and broad application support.

The SN74LV138AD belongs to TI's LV logic family, engineered for low-voltage, high-speed operation across mixed-signal industrial and computing systems - specifically targeting memory expansion, display control, and digital signal routing where timing precision and power sequencing matter.

FAQ

What is the maximum propagation delay of the SN74LV138AD at 3.3 V operation?

The SN74LV138AD exhibits a maximum propagation delay of 13.5 ns at VCC = 3.3 V with a 15 pF load and TA = 25°C, as specified in Section 6.7 of the official datasheet. This value reflects worst-case timing across process, voltage, and temperature corners, ensuring reliable setup/hold margins in 3.3 V systems.

Does the SN74LV138AD support partial power-down, and how is it implemented?

Yes, the SN74LV138AD supports partial power-down via its Ioff feature. When VCC is driven to 0 V, internal circuitry disables all outputs, limiting leakage current to ≤5 μA per I/O pin. This prevents damaging back-current flow in multi-rail systems - a verified capability confirmed in Section 6.5 and 8.3.3 of the SN74LV138AD datasheet.

Can the SN74LV138AD be used with both 2.5 V and 5 V logic families in the same system?

Yes, the SN74LV138AD supports mixed-mode voltage operation: its inputs tolerate up to 5.5 V regardless of VCC, and outputs swing rail-to-rail. At VCC = 2.5 V, it reliably accepts 5 V inputs and drives 2.5 V-compatible loads - confirmed by VI and VO ratings in Section 6.1 and 6.3 of the SN74LV138AD datasheet.

What is the recommended bypass capacitor for the SN74LV138AD VCC pin?

Texas Instruments recommends a 0.1-μF ceramic capacitor placed physically adjacent to the VCC pin of the SN74LV138AD, with short, low-inductance traces to GND. This value is specified in Section 9.3 and validated in layout examples (Figure 9-3) to suppress high-frequency supply noise and maintain stable switching performance.

How many enable inputs does the SN74LV138AD have, and what are their logic polarities?

The SN74LV138AD has three enable inputs: G0 and G1 are active-low, while G2 is active-high. All three must satisfy their respective logic states simultaneously for any output to activate - a configuration explicitly defined in the Function Table (Section 8.4) and leveraged for hierarchical decoding without external inverters.